The long range aim of the project is to define the cellular and molecular mechanisms regulating the contractile element of airway smooth muscle. Three biochemical pathways that could modulate the contractile element of airway muscle will be investigated; myosin phosphorylation, the Ca2+, phospholipid-dependent protein kinase, and the cAMP-dependent protein kinase. Canine tracheal smooth muscle will be the model of airway smooth muscle used to achieve the following aims: I. Define the role of myosin phosphorylation and Ca2+ in regulating the crossbridge kinetics of airway smooth muscle by determining the effect of varying Ca2+ on shortening velocity. II. Test the hypothesis that muscarinic stimulation of airway muscle promotes phosphorylation of the 20,000 dalton myosin light chains by activation of C-kinase. Peptide maps of the phosphopeptide(s) formed during muscarinic activation will be compared to the phosphopeptides formed during activation with potassium and histamine. III. Test the ability of phorbol esters, agents that activate C-kinase, to promote phosphorylation of myosin in intact tracheal muscle. IV. Develop a chemically skinned tracheal muscle preparation to test the hypothesis that activation of cAMP-dependent protein kinase will relax airway muscle at low Ca2+ concentrations by dephosphorylation of myosin. The results will improve our understanding of the cellular events mediating airway smooth muscle tone, and will contribute to the general understanding of smooth cell physiology. The results may also have implications for therapy of respiratory disease. Physiological antagonism of airway muscle contraction is the principle therapeutic strategy in relaxing hyper-reactive airways, and improved understanding of the molecular mechanisms of airway muscle contraction and relaxation may identify new targets for drug action.